Frenzel, born on 20 August 1911 in Zehdenick on the Havel, the son of a Reichsbahn employee, both his brothers were killed in the First World War. He took on a four year apprenticeship as a carpenter, but work in this field was difficult to find. He managed to find agricultural work, then became a driver for a butcher. He joined the Nazi Party and became an SA man from August 1930, and his fervent belief in National Socialism , he received a dagger of honour from Hitler personally, which he described as “his greatest experience.“
At the end of 1939 he was employed by T4 and Frenzel first went to Grafeneck institution where he worked as a guard, he then went to another institution at Bernburg and then onto Hadanar, where he became involved in the gassing and cremating of mentally ill and disabled people . After returning to Bernburg to help dismantling the gassing facilities, in mid-April 1942 he was summoned to Berlin and together with other old comrades from other T4 institutions were ordered to report to Odilo Globocnik, SS-und Polizeiführer Lublin. Frenzel was given the rank of SS- Oberscharführer and was posted to Sobibor, and he arrived there on 28 April 1942.
After a short while Frenzel was placed in charge of Lager I and the Bahnhofskommando, he was the one alongside Gustav Wagner , who selected the workers who were to live whilst the rest were consigned to the gas chambers. SS- Scharführer Erich Bauer , who served with Frenzel in Sobibor, recalled; “He (Frenzel) was one of the most brutal members of the permanent staff in the camp. His whip was very loose.” Eric Bauer died at Berlin Tegel prison on February 4, 1980, age 79 and in October 1980, Wagner was found with a knife in his chest in Sao Paulo. According to his attorney, Wagner committed suicide ?. His date of death was determined to be 3 October 1980, age 69.
Frenzel, was one of the main targets of the prisoners during the revolt on 14 October 1943, but he escaped because he was in the shower. Because Franz Reichleitner was absent and deputy commandant Johann Niemann was killed by the prisoners,
Frenzel took command of the camp in the aftermath of the revolt. Reichleitner was killed by partisans on 3 January 1944, age 37, at Fium, Italy. Niemann was killed, 14-October 1944, age 30 in the tailor’s barracks with an axe to his head by Alexander Shubayev , a Jewish Red Army soldier imprisoned at Sobibór as Sonderkommando slave labourer.
Once Sobibor death camp had been dismantled and closed down, he was sent to join Globocnik in Trieste. He was assigned to Sondertruppe R as a Polizeihauptwachtmeister in Trieste and Fiume, hunting Jews and fighting partisans. In the spring of 1944 he was involved in a motor accident and spent a long time in a hospital in Udine. After being captured by the American forces he was taken to a Prisoner of War camp in the Munich area and made his way back to his home in Lowenburg in November 1945, the very day his wife Sofia died. He found employment as acting stage manager for a film studio in Gottingen. Frenzel was arrested for war crimes committed at Sobibor on 22 March 1962 and following a trial in Hagen he was sentenced on 20 December 1966 to life imprisonment. Karl Frenzel died in a retirement home in Garbsen / Hanover on 2 September 1996.